Feral Hog Toxicant

ABSTRACT

A composition and method for killing feral hogs: a bait that is attractive to hogs is mixed with a lethal amount of sodium nitrite, along with sufficient base to inhibit decomposition of the sodium nitrite. At sufficiently high pH, encapsulation of the sodium nitrite is not required to inhibit decomposition. In the absence of substantial decomposition, the sodium nitrite itself is not aversive to the pigs, and may even enhance acceptance of the baits by the pigs. Optionally, an anti-emetic compound is added to the mixture to reduce the likelihood the bait will be vomited. Optionally, an additional toxicant such as luteolin is added to the mixture.

This application is a divisional of co-pending application serial number17/000,581, filed Aug. 24, 2020, now allowed with the issue fee paid;which claimed the benefit of the Sep. 6, 2019 filing date of provisionalpatent application serial number 62/896,779 under 35 U.S.C. § 119(e).The complete disclosures of both priority applications are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

This invention pertains to compositions for killing feral hogs, methodsfor making such compositions, and methods of using such compositions.

BACKGROUND ART

Wild pigs, or feral hogs (Sus scrofa) damage crops across the UnitedStates, with annual losses estimated at $1.5 billion. Wild pigs alsopose a significant risk to human health. Data suggest that they carryzoonotic diseases, potentially affecting humans and other mammals, withsome pathogens that can be transferred to surface waters. Zoonoticdiseases carried by wild pigs include anthrax, bovine herpes virus,bovine tuberculosis, brucellosis, campylobacteriosis, colibacillosis (E.coli), various coronaviral infections, cysticercosis, echinococcosis,encephalomyocarditis, erysipelas, foot and mouth disease, helicobacter,hepatitis E, influenza A, influenza D, Japanese encephalitis,leptospirosis, listeriosis, louping-III virus, menangle virus,papillomavirus, parainfluenza virus, plague, pseudorabies, Q fever,rabies, ringworm, salmonellosis, sarcocystosis, scabies, shigellosis,staphylococcosis, stephanuriasis, streptococcosis, toxoplasmosis,trichinellosis, tularemia, vesicular stomatitis, West Nile virus, andyersiniosis. However, pigs do not appear to be carriers of SARS-CoV-2.Wild pigs have also been documented to attack humans, often unprovoked,although such attacks are relatively uncommon.

Current methods to control feral swine include trapping, hunting,shooting, and snaring, depending on local laws. However, the populationof this invasive species continues to increase. Wild pigs reproduce sorapidly that shooting and trapping are ineffective means of populationcontrol. Other previous efforts to control feral swine have had poorresults.

Feral swine reproduce so rapidly that it is estimated that about 70% ofthe current population would need to be removed each year, just to holdthe population constant. Such a high level of control is difficult toachieve by hunting and trapping alone.

Sodium nitrite in high doses is lethal to pigs, but it has previouslybeen difficult to use as a toxicant for hogs. Sodium nitrite imparts abitter taste to baits, and the bitterness makes pigs avoid the baits.One approach to this problem has been to microencapsulate the sodiumnitrite, to minimize its effect on a bait’s taste. Whilemicroencapsulation can be effective, microencapsulated formulations arerelatively expensive, and the thin encapsulation layers can degradeunder humidity and temperature conditions often encountered in thefield.

To the inventors’ knowledge, there have been no previous reports of anyeffective, sodium nitrite-based hog toxicant, that has successfully usedan approach other than encapsulation to mitigate the bitter tasteassociated with nitrite. Although encapsulation can be effective, itadds to the expense.

If an inexpensive solution were available for the problem of bittertaste, sodium nitrite would be a preferred toxicant to use against hogs.Although sodium nitrite is not species-specific for hogs, hogs areespecially sensitive to sodium nitrite, with a much lower LD₉₀ than thatof many other wildlife species. Also, the effects of sodium nitrite arenot cumulative, meaning there should ordinarily be no long-term adverseeffects if a non-target species incidentally eats a small amount of asodium nitrite-containing bait intended for pigs - e.g., crumbs left onthe ground.

Furthermore, over time sodium nitrite will break down in mostenvironments (even when administered in accordance with the novelformulation described herein), so it should not linger in theenvironment as a long-term toxic residue.

L. Shapiro et al. (2015). Efficacy of encapsulated sodium nitrite as anew tool for feral pig management. Journal of Pest Science. 89.10.1007/s10340-015-0706-7 disclose the use of encapsulated sodiumnitrite in a palatable paste matrix bait to provide a lethal dose toferal pigs.

Snow et al. (2017). Potential secondary poisoning risks to non-targetsfrom a sodium nitrite toxic bait for invasive wild pigs. Pest Manag Sci.DOI 10.1002/ps.4692 disclose the use of microencapsulated sodium nitriteformulations as the active ingredient in a bait matrix for controllingferal hogs; and the secondary effects of such baits on non-targetspecies. The encapsulated formulations were described generally as oneof the following: a water-soluble protein coating, a double coating ofthe water-soluble protein, a soft wax coating insoluble in water, or anacidic resistant resin designed for enteric release of pharmaceuticals.

US Pat. No. 8,795,649 discloses the use of baits with nitrite salts suchas sodium nitrite to control feral animals such as feral pigs.

WO2010151150A2 reported that adding omeprazole (a proton pump inhibitor)to a microencapsulated sodium nitrite-containing bait had a slight, butnot significant, effect upon toxicity and subsequent time to death forpigs.

B. Thompson and Pojman Research Team, “Encapsulation of Sodium Nitrite,”slides of presentation given at LSU Idlewild Research Center (Sep. 15,2018) gives some preliminary results from work carried out by theinventors and their colleagues concerning the encapsulation of sodiumnitrite as a potential hog toxicant; and possible alternatives toencapsulation such as treatment with baking soda or essence of rottingfish.

See also the following presentations of work carried out by theinventors and their colleagues: G. Gentry, “Development of ControlOptions for Feral Swine in Soybean Fields,” presentation made toLouisiana Soybean and Grain Research and Promotion Board, Baton Rouge,LA, Nov. 21, 2019; G. Gentry, “Development of an Encapsulation Protocolfor Sodium Nitrite for Control of Feral Swine in Rice,” presentationmade to Louisiana Rice Research Board, Crowley, LA, Oct. 7, 2019; G.Gentry, “Management and Control of Feral Hogs,” presentation made toSouthern Section of Weed Science Society, Biloxi MS, Jan. 27, 2020; andG. Gentry, “Feral Swine Toxicant Update,” presentation made to Bob RJones Wildlife Research Institute Board Meeting, Clinton, LA, Feb. 20,2020.

There is an unfilled need for improved compositions and methods tocontrol feral swine populations.

SUMMARY OF THE INVENTION

We have discovered an improved composition and method for killing feralhogs. Briefly, a bait that is attractive to pigs is mixed with a lethalconcentration of sodium nitrite, along with sufficient base (alkali) toinhibit decomposition of sodium nitrite. Encapsulation of the sodiumnitrite is not required if the pH is sufficiently high to inhibitdecomposition. When decomposition is minimized, we have found that,contrary to conventional wisdom, sodium nitrite itself is actually notaversive to pigs. Rather, we found that it is only the decompositionproducts of sodium nitrite that are aversive to pigs, decompositionproducts that can be avoided by avoiding acidic conditions. By using ahigher pH, such decomposition is minimized. Optionally, an anti-emeticcompound is added to the mixture to reduce the likelihood that the baitwill be vomited. Optionally, an additional toxicant such as luteolin isadded to the mixture.

The present invention provides a toxicant that can effectively targetwild pigs, with low impact on non-target species. Sodium nitrite isdelivered in a form that resists the rigors of the environment, in abait station or otherwise, without imparting a bitter flavor that couldmake the bait repellent to hogs. After the bait is consumed, theformulation releases a lethal dose of sodium nitrite in the pigs’digestive tract. The invention will help reduce the wild pig population,will help reduce damage to crops caused by pigs, will help reduceenvironmental destruction by pigs, and will help reduce the incidence ofzoonotic diseases spread by pigs.

LD₉₀ for sodium nitrite in adult hogs is about 189 mg / kg. Our earlierapproach to address the problem of sodium nitrite bitterness had been toseek improved encapsulation formulations for sodium nitrite. Whileencapsulation methods can work, in the course of this work wediscovered, quite unexpectedly, that encapsulation was not needed. Bycontrolling the pH of the formulation, encapsulation becomesunnecessary.

One bait formulation used in prototype trials contained dehydrated fish.The sodium nitrite was added to a potato dextrose agar mixture withground fish. Hogs ate this bait and were poisoned by the nitrite. Trialswill also be conducted using alternative bait ingredients that are alsoappealing to pigs. These baits will be compared with whole-shelled corn,which serves as the control, a standard for all comparisons ofacceptance and consumption by pigs.

Vacuum-packing the baits until they are used is optional, and ispreferred to enhance shelf life. Refrigeration or freezing is anotheroptional step that can also enhance shelf life.

The lethal dose should be delivered to the pigs in a very short periodof time, preferably as a bolus. If the toxicant delivery is spread out-even over a time as short as one hour - its efficacy can be greatlyreduced or lost entirely. The effects of sodium nitrite are notcumulative over time; the toxicant should be delivered to each pigessentially all at once or over a very short period of time.

Unexpectedly, we discovered that raising the pH inhibits decompositionof the nitrite, without the need to encapsulate the nitrite. We foundthat by raising the pH, it became unnecessary to encapsulate nitrite toinhibit decomposition in a bait used as a hog toxicant.

Contrary to prevailing wisdom, we have discovered how to incorporatesodium nitrite into effective hog baits without the need forencapsulation, and without imparting a bitter taste that repels hogsfrom a bait, by maintaining at least a neutral pH, or preferably a basicpH. Sodium nitrite itself is actually not bitter. NaNO₂ only acquires abitter taste as it decomposes in response to the environment. Whensodium nitrite is not exposed to moisture or to acidic pH levels, itdoes not itself have a bitter taste, and indeed its taste is nearlyidentical to that of sodium chloride, common table salt.

Encapsulation may optionally also be employed, along with raising thepH, to further enhance the effective lifetime of baits in the field -but our discovery makes encapsulation unnecessary. The effectivelifetime of baits in the field can be enhanced by both encapsulating thesodium nitrite and raising the pH of the sodium nitrite or of the baitas a whole, but in many circumstances it will not be advantageous oreconomical to do so.

The pH of the bait inhibits the decomposition of sodium nitrite, suchthat when the bait is placed outdoors in the field or in a bait stationunder ambient conditions, any decomposition of the sodium nitrite issufficiently slow that the bait does not become aversive to hogs for atleast seven days, and will readily be eaten by feral hogs for at leastseven days. The effective lifetime of baits in the field will of coursevary, depending on the prevailing ambient conditions. The compositionshould inhibit decomposition (to a point where it becomes aversive tohogs) for at least seven days when the ambient conditions includedaytime temperatures of 45° F. or greater, 50° F. or greater, 55° F. orgreater, 60° F. or greater, 65° F. or greater, 70° F. or greater, 75° F.or greater, 80° F. or greater, 85° F. or greater, 90° F. or greater, or95° F. or greater; and when the ambient conditions include a daytimerelative humidity that at least at times is 40% or greater, 45% orgreater, 50% or greater, 55% or greater, 60% or greater, 65% or greater,70% or greater, 75% or greater, 80% or greater, 85% or greater, 90% orgreater, or 95% or greater.

We have observed that deer tend not to eat baits in accordance with thepresent composition. Bears however will eat the baits, but proper designand use of a bait station can help minimize off-target consumption bybears. Other non-target species that have not yet been tested includeraccoons, opossums, birds, dogs, and cats.

The pH of the bait should be 7 or higher to inhibit decomposition ofsodium nitrite into bitter products. It is preferred that the pH shouldbe higher than 7. It is particularly preferred to incorporate analkaline material into the bait, such as calcium carbonate or sodiumbicarbonate, that can neutralize stomach acid and inhibit vomiting. ThepH can be 7 or greater, 7.5 or greater, 8 or greater, 8.5 or greater, 9or greater, 9.5 or greater, 10 or greater, 10.5 or greater, 11 orgreater, 11.5 or greater, 12 or greater, or 12.5 or greater. Preferably,the pH of the bait is from 8 to 11. Although a pH of 7 is marginallyacceptable, a slightly higher pH, e.g., 8 or higher, is preferred tocounteract acidity from carbon dioxide in the air. A pH of 8 to 11, or 8to 12, can also help inhibit vomiting of the baits.

Egg whites can be alkaline. In an alternative embodiment, egg white maybe incorporated into the bait, in lieu of or in addition to some or allof the inorganic alkaline salt. When chicken eggs are first laid, the pHof the albumen (egg white) is nearly neutral, but over time the pH ofthe albumen can rise to around 9.3-9.5.

In accordance with standard food science procedures, the pH of a baitmaterial may be determined by grinding it into a paste, and insertingthe probe of an ordinary pH meter into the paste to directly measure thepH in the otherwise usual manner. If the bait is too dry to givereliable readings in this way, then the ground bait may be moistenedwith a sufficient quantity of deionized water to enable the pH meter andprobe to take reliable measurements within the resulting paste.

Potato dextrose agar (PDA) is a weak acid, pH ~5, as are other commonmaterials that might typically be used in a bait. On its own, sodiumnitrite is not a strong enough base to overcome the acidity of a PDAmatrix, and additional basic materials should be incorporated into thebait to raise the bait’s pH.

The pH of the bait matrix is controlled so that, until the bait isconsumed, the sodium nitrite is only in contact with neutral or(preferably) alkaline mixtures. At non-acidic pH, no bitter flavordevelops. Indeed, the resulting salty flavor results in a bait thatactually seems to be preferred by feral hogs over control baits lackingsodium nitrite. Ironically, at higher pH the lethal sodium nitrite canactually increase hogs’ consumption of the bait as compared to anotherwise identical bait lacking sodium nitrite.

Optionally, monosodium glutamate (MSG) can also be incorporated into thebait, to further increase its acceptance by hogs. MSG enhances the“umami” flavor. MSG can attenuate the sweetness of components such aspotato dextrose agar, and it may somewhat attenuate the saltiness of thenitrite itself, in addition to imparting a meaty flavor. Alternatively,monopotassium glutamate (MPG) can provide an umami flavor withoutincreasing sodium levels. Because MSG adds sodium while MPG does not, itis possible that MPG could assist in avoiding the upper limit ofsaltiness that hogs are willing to eat, although this possibility hadnot yet been tested as of the filing date of this patent application.Either of these additives (MSG or MPG) can help increase the levels ofsodium nitrite that can be loaded into baits, while retaining a flavorthat hogs find acceptable. Optionally, other nitrite salts may be usedin lieu of sodium nitrite, e.g., potassium nitrite, calcium nitrite,magnesium nitrite, lithium nitrite, or ammonium nitrite.

Another difficulty of using sodium nitrite as a toxicant is that feralhogs can sometimes vomit the baits. The acidic decomposition of sodiumnitrite in gastric juices can lead to the release of noxious, gaseousbyproducts that can induce vomiting. This tendency can be counteractedby incorporating into the bait antiemetic compounds, antacid compounds,or both. Antacids include such compounds as sodium carbonate, sodiumbicarbonate, calcium carbonate, magnesium hydroxide, magnesiumcarbonate, potassium carbonate, amines (e.g. from fish), and potassiumbicarbonate. Antacids such as sodium carbonate also help maintain ahigher pH level before the bait is consumed. Then after consumption theantacids can help neutralize gastric acid, both inhibiting the breakdownof sodium nitrite in vivo, and also helping to reduce vomiting. Ourpreliminary results have shown that sodium carbonate is effective inreducing vomiting after toxicant baits are consumed. Anti-emetics canalso be employed, for example taste-free ginger extracts containinggingerols. Gingerols directly inhibit vomiting via pharmacologicalaction on serotonin type-3 receptors in the digestive system. Gingerolshave the same mechanism of action as drugs such as Zofran (ondansetron),which are prescribed in humans for the treatment of severe,chemotherapy-induced nausea. Other anti-emetics known in the art mayalso be used.

An optional embodiment enhances the effective of sodium nitrite byincorporating the flavonoid luteolin into a bait. Luteolin is found inbotanical sources including celery, broccoli, green pepper, parsley,thyme, dandelion, perilla, chamomile, carrots, olive oil, peppermint,rosemary, oranges and other citrus, oregano, and certain palm seeds. Themechanism of sodium nitrite toxicity is to oxidize hemoglobin in theblood to methemoglobin, converting the iron atom from the ferrous formto the ferric form. Methemoglobin has a poor ability to transport oxygento cells. Methemoglobin is naturally present in mammalian blood at 1 -2% of total hemoglobin, a level that is ordinarily tempered by the enzymemethemoglobin reductase (MR). One factor that makes sodium nitritewell-suited for killing hogs is that hogs naturally possess lower levelsof MR than do humans and many other mammals. Because hogs have a poorability to detoxify methemoglobin build-up, they are inherently moreprone to developing high concentrations of methemoglobin upon exposureto sodium nitrite, which can quickly lead to death. In an optionalembodiment, this physiology is further exploited by incorporating MRinhibitors into the bait, thus facilitating control of feral hogs whilereleasing less total nitrite into the environment. Luteolin is ahighly-potent, commercially-available, naturally-occurring, tasteless MRinhibitor. Adding small amounts of luteolin to a nitrite-containing baitwill reduce a hog’s ability to detoxify methemoglobin. Thus the baitscan have enhanced potency with less total toxicant. The water solubilityof luteolin increases as the pH increases, due to ionization of phenolichydroxyl groups. Luteolin is poorly soluble at neutral or acidic pH. Thehigher pH of the baits used in this invention is compatible withluteolin.

As of the filing date of this patent application, we do not yet havedata on the incorporation of luteolin into baits. Following are somepreliminary guidelines until experimental data become available; theguideline amounts may readily be adjusted based on experimentalmeasurements of effectiveness: The IC₅₀ for luteolin is about 0.11micromolar. Assuming there are about 65 mL blood per kilogram body massin the pig, the amount of luteolin needed for 50% inhibition of the MRenzyme should be about ~2 micrograms per kilogram body mass. Assuming anconservative bioavailability as low as 0.1%, a guideline amount toadminister is 2 milligram luteolin per kilogram of pig body mass. For a150 kg pig, roughly 300 milligrams of luteolin should inhibit MR by 50%.We expect 300-1000 mg luteolin per bait should be an effective dose.Luteolin is inexpensive and tasteless, and it should not affectacceptability of the bait to pigs.

Other MR inhibitors could also be used, in addition to or in lieu ofluteolin. For example, some anthoxanthins or their bioconjugates (e.g.,luteolin-7-O-glucoside) act as MR inhibitors, and these compounds may beincorporated into the bait.

It is preferred to take simple steps otherwise known in the art toenhance the shelf life of baits generally - for example, one or more ofvacuum packing, refrigeration, or freezing.

Hog behavior is such that hogs may naturally tend to hoard baits,tending to keep them from one another. One possible method ofadministration that can both help counteract this tendency, and alsohelp reduce potential exposure of non-target species, is to bury thebaits in the ground, spaced at least 4 to 5 feet apart. The pigs’natural rooting behavior will tend to lead them to the baits; thespacing will tend to reduce hoarding; and burying the baits will tend tolimit exposure to non-target species.

MODES FOR CARRYING OUT THE INVENTION Example 1: Feral Hog Toxicant WithIncreased pH

To a 2 L beaker was added 1500 mL deionized water. The beaker with waterwas heated to boiling, and 117 g potato dextrose agar (PDA) was slowlyadded under 2000 rpm mechanical stirring. Once the mixture washomogeneous, the PDA solution was cooked in a pressure cooker for 15minutes on the pressure cooker’s “brown rice” setting (15 psi and 240°F.). After cooking, the mixture was transferred back into the 2 L beakerand stirred at 1500 rpm. During the stirring, 45 grams of ground,dehydrated fish was added, along with 10 grams of the base sodiumcarbonate. Sodium nitrite (150 grams) was added under stirring once thefish / PDA mixture had reached a temperature of 55° C. After mixing wascomplete, a garden syringe was used to quickly transfer the completedbait matrix into spherical, 50 mL molds. The filled molds were placed ina freezer, and the baits were packaged after they had frozen.

Examples 2 and 3: Feral Hog Toxicant With Encapsulated Sodium NitriteEthocel™ Encapsulation

A pan coating device equipped with a nitrogen drying line was chargedwith 1 kg sodium nitrite. A solvent containing 80:20 (mass ratio)acetone : ethanol was used to prepare a 10 weight-percent solution ofDOW Ethocel™ Standard 10 (ethylcellulose polymer). To the solventsolution was added 1% glycerol by total solution mass. All componentswere stirred until homogeneous, and the mixture was then placed into ahandheld spray bottle. The Ethocel™ coating solution was applied to thesodium nitrite as it tumbled in a coating drum. Nitrogen gas was pipedinto the drum to facilitate drying. Successive coats were applied untilthe desired coating thickness had been reached. After the last coat wasapplied, the encapsulated sodium nitrite was tumbled until dry and thenstored until use.

Shellac Encapsulation

A pan coating device equipped with a nitrogen drying line was chargedwith 1 kg sodium nitrite. Zinsser Bullseye™ aerosol shellac was appliedto the sodium nitrite as the sodium nitrite tumbled in the coating drum.Nitrogen gas was piped into the drum to facilitate drying. Successivecoats were applied until the desired coating thickness was reached.After the last coat had been applied, the encapsulated sodium nitritewas tumbled until dry and then stored until use.

These encapsulated sodium nitrite preparations are also toxic againsthogs (data not shown).

Examples 4 and 5 Prototype Trials Using Un-Encapsulated, High-pH SodiumNitrite Baits on Feral Swine

Two sets of trials were conducted on wild-captured feral swine at theBob R. Jones Idlewild Research Station (Clinton, LA) from December 2018through September 2019. Pigs were offered two-inch spheres generallycontaining (depending on the trial) twice the lethal dose of 189 mgsodium nitrite per kg of the pig’s body weight, using baits prepared bythe method described in Example 1. Multiple pigs were used in someindividual trials, to increase competition between animals, in anattempt to increase bait consumption per animal. Most pigs died if theyconsumed at least half the bait offered. Pigs survived when theyconsumed no bait, or less than half the bait offered.

The first set of trials used pigs individually housed under roof in 3.5m × 3.5 m holding pens. The purpose of these experiments was todetermine the acceptance and preference of feral swine for theunencapsulated sodium nitrite baits, in the absence of competitionbetween animals. The pigs (N=7) were weighed and were offered a choiceof baits containing a lethal dose of unencapsulated sodium nitrite,otherwise identical control baits lacking sodium nitrite, or wholeshelled corn. We observed that the pigs consumed 63% of the sodiumnitrite-containing baits, 30% of the baits lacking sodium nitrite, and43% of the whole shelled corn. In other words, the pigs affirmativelypreferred the baits with the sodium nitrite toxicant. 57% of the pigsconsumed more sodium nitrite-containing bait than any other treatment.86% of the pigs consumed more sodium nitrite-containing bait thanwhole-shelled corn. 29% of the pigs consumed all of the sodiumnitrite-containing baits, resulting in a 100% death rate in thoseinstances. Overall, 43% of all the pigs consumed enough sodium nitriteto result in a lethal outcome. The average time to death was about 120minutes.

A second set of trials (N=18) assessed whether competition among pigswould affect consumption rates. For each trial, two to four feral pigswere housed under a single roof in 3.5 m × 3.5 m holding pens. Pigs wereweighed, and sufficient number of sodium nitrite-containing baits wereoffered to provide a lethal dose for all pigs in the pen. The overalldeath rate in these trials was 39%. 21% of the sodium nitrite-containingbaits were consumed. 50% of the trials had a mortality rate 50% orhigher. 13% of the trials had 100% mortality. The average time to deathwas about 228 minutes.

From these trials we reached several conclusions: that the sodiumnitrite-containing baits can effectively deliver a lethal dose of sodiumnitrite to feral hogs; that the pigs do not avoid the baits; that indeedthe pigs affirmatively prefer the lethal baits, at least in some cases;and that it is preferred to deliver the baits to pigs in a manner thatreduces competition among pigs for the baits (for example by dispersingthe baits over a wider area), so that a higher percentage of pigs in agroup will consume a lethal dose.

Example 6 Effects of Age and Sex of Pigs on Bait Consumption

As of the filing date of this patent application, we had not yetconducted experiments concerning the effects of the age and sex of pigson bait consumption. However, based on past observations of ovine socialbehavior in general, we presume that social dominance order within asounder (herd, group) will likely plays a role in who eats the baitsfirst, and how much individual pigs will consume. Ideally, all pigs thatshow up should eat enough bait to consume a lethal dose. Typically,older males would be highest in social dominance. But male feral pigsusually travel alone or in bachelor groups. Within a sounder thematriarch female, the oldest female, is generally the first to eat andeats the most. A sounder typically has two older female pigs, andbetween 6 and 20 juveniles. In general, the heavier the pig the higherits social rank, and the more it eats. It is preferred to separate thedelivery of baits, either spatially or temporally, to increase thenumber of pigs within a sounder consuming a lethal dose of the baits.

Example 7. Modified Formulation of Un-Encapsulated, High-pH SodiumNitrite Baits

As shown in the data of Examples 4 and 5, baits made by the method ofExample 1 were effective in supplying a lethal dose of sodium nitrite tohogs. However, we observed that in use these baits would sometimes fallapart after they had been removed from a 0° C. freezer and thawed.Although the baits were still effective, they were less convenient touse. Besides the inconvenience factor, a frangible bait is more likelyto be incompletely consumed by the target hogs, and to leave uneatenpieces behind that might be consumed by non-target species. We areuncertain why these baits became frangible.

We modified the formulation to enhance physical integrity of the baitsafter thawing. The formulation of Example 1 had used potato dextroseagar. In the modified formulation we replaced the potato dextrose agarwith pure agar (purchased from Sigma Aldrich). Pure agar was chosenbecause it is a tasteless polymer that remains a gel withoutdegradation, depending on the particular formulation, typically up toabout 40° C. Sugar (sucrose, purchased from Walmart) was also added inthis formulation to further reduce any bitterness. This formulation wasnot autoclaved, as the sodium nitrite itself can act as a preservativeagainst many bacteria and other microbes. Initial trials suggested thata 2.5% (w/w) agar solution produced baits with adequate stiffness andresilience - almost a rubbery texture. These 2.5% (w/w) agar baits wereused in tests conducted in the summer months in south Louisiana.

More specifically: 750 g deionized water was heated to boiling. Once thewater was boiling, it was transferred to a 1500 mL glass beaker set on a270° C. hot plate. 100 g of commercially-purchased sugar (sucrose) wasadded, and stirred with an immersion blender at a low setting. After thesugar had dissolved, 19.3 g of powdered agar was added, and the mixturewas stirred with the immersion blender at a medium setting. The opaquereaction mixture was left on the hot plate for 15 minutes, and themixture was sheared with an overhead stirrer at 800 rpm until themixture became clear. The mixture was removed from the heat source.After it had cooled to around 75° C., 22.5 g of dried pogie fish(Brevoortia patronus) and 5 g sodium carbonate were added to themixture, with shearing from the immersion blender at a medium setting.Finally 195 g sodium nitrite were added to the mixture once thetemperature had dropped to 60° C., and the mixture was mixed thoroughlyfor a few minutes with the immersion blender before it was poured intomolds. The molds were left undisturbed for about 30 minutes. The mixturethen solidified or gelled. The molds were transferred to a refrigeratorto cool and gel further overnight. The solidified baits were removedfrom the molds and stored at 4° C. in Ziploc™ bags until they were used.

The modified baits were found to be stable both when refrigerated, andwhen stored at room temperature. It is preferred to store the baits at4° C. or to keep them frozen. After being kept in a freezer for 20 days,the thawed baits remained intact after thawing and being held at roomtemperature for several days. The modified formulation fragmented muchless than the formulation of Example 1, and is therefore more likely tobe completely consumed by the pigs, and less likely to produce smallpieces that might be eaten by birds or other non-target species.

The complete disclosures of all references cited in this specificationare hereby incorporated by reference in their entirety, as is thecomplete disclosure of priority application serial number 62/896,779. Inthe event of an otherwise irresolvable conflict, however, the disclosureof the present specification shall control.

What is claimed:
 1. A composition comprising a mixture of: (a) a foodthat is acceptable to feral hogs; (b) sodium nitrite, wherein saidsodium nitrite is not microencapsulated; and (c) a base selected fromthe group consisting of sodium carbonate, sodium bicarbonate, calciumcarbonate, magnesium hydroxide, magnesium carbonate, potassiumcarbonate, potassium bicarbonate, egg white albumin, and an amine;wherein the concentration of said base imparts a pH between 8 and 11 tosaid mixture; wherein said composition is supplied as a bolus orboluses, comprising at least 2.0 gram sodium nitrite per bolus; whereinthe pH of said composition inhibits the decomposition of said sodiumnitrite, such that when said composition is placed outdoors in a fieldor in a bait station under ambient conditions, any decomposition of saidsodium nitrite is sufficiently slow that said composition does notbecome aversive to hogs for at least seven days; and wherein, for atleast seven days, when placed outdoors under ambient conditions, saidcomposition remains acceptable to feral hogs.
 2. The composition ofclaim 1, wherein said mixture additionally comprises at least 300milligram luteolin per bolus.
 3. The composition of claim 1, whereinsaid mixture additionally comprises monosodium glutamate, monopotassiumglutamate, or both.
 4. The composition of claim 1, wherein each boluscomprises at least 8.0 gram sodium nitrite.
 5. The composition of claim1, wherein said mixture additionally comprises an antiemetic compound.6. The composition of claim 1, wherein the pH of said compositioninhibits the decomposition of said sodium nitrite, such that when saidcomposition is placed outdoors in a field or in a bait station underambient conditions, any decomposition of said sodium nitrite issufficiently slow that said composition does not become aversive toferal hogs for at least seven days, and will readily be eaten by feralhogs for at least seven days; wherein the ambient conditions to whichsaid composition is capable of being exposed include daytimetemperatures of 90° F. or greater, and a relative humidity of fiftypercent or greater.